The present invention relates to a method of continuously marking material which is to be moved in its longitudinal direction, wherein annular markings of limited axial extent are applied to the surface of the material by jets of ink (color) which emerge under pressure from at least two nozzles which are parallel to each other and swing continuously around an axis of swing. The jets impinge on the surface of the material at a right angle to its direction of movement, and the nozzles are supplied with ink by a common pump via a feedline (West German Patent 14 65 660).
"Elongated material" within the meaning of the invention comprises, for instance, electric lines, such as control lines or else insulated wires of communication cables to which the following remarks refer, by way of example, to all other applications.
The color marking of wires is required for communication cables so as to permit easy identification of individual wires for installation. Thus, for instance, in the case of four wires which are to be stranded into a quad, rings are sprayed onto the insulation of three of said wires, each wire being marked differently. The fourth wire remains unmarked. The marking of the three wires can be effected in the manner that the first wire is marked with single rings, the second wire with double rings spaced a short distance apart and the third wire with double rings spaced a larger distance apart, or that the wires ar provided with markings of a different color. The individual markings are applied at uniform distances apart.
The aforementioned German Patent 14 65 660 describes a method in which a device is used which has become known under the commercial name "Colormat". By means of this device the markings are sprayed onto the wires of the conductors immediately after the application of the insulating material to the wires. The ink jets therefore impinge on a relatively hot insulation so that the ink dries quickly and is firmly bonded to the insulating material. In this known method, two nozzles are used, which are arranged parallel to each other and produce on the insulation of a wire two rings which are a fixed distance apart from each other. If this type of marking of the wire is to be changed to only one ring, then either a new nozzle system with only one nozzle must be installed or the feeding of ink to one of the two nozzles must be interrupted. The changing of the nozzle system is time-consuming as production must be halted, while a second nozzle system means increased costs. If in the case of a nozzle system having two parallel nozzles the feeding of ink to one nozzle is interrupted, problems also result since the entire quantity of ink delivered by the common pump is now fed to the one nozzle which is still open. Due to the now increased speed of discharge of the ink jet from the nozzle, the wave length of the jet is increased. This leads to an impermissible change in the markings sprayed on the wire.